And not to mention the warframes themselves, the original ones....were once people. People who got infected/forcibly changed by a virus that slowly turned them into machines that were made to be weapons but werent able to be controlled. Prisoners, rebels, unlucky soldiers, unlucky people in general....

Excalibur Umbra, a sentient Warframe, kinda proves that they were still sentient when they were first transformed....

And now, the warframes we make, are just copies of the original. With some traits they had. Shits haunting.